1. Field of the Invention
The present invention relates to a data transmission device and a data transmission method and, more particularly, to a data transmission device and a data transmission method that transmit parallel data.
2. Description of Related Art
Data transmission devices transmit parallel data from a transmission side to a reception side.
For example, in a liquid crystal display device (hereinafter as ‘LCD module’), 6-bit or 8-bit parallel data is used as data for each of red (R), green (G) and blue (B) colors. The parallel data for each color is transmitted from a control LSI at the transmission side to a driver LSI at the reception side.
More specifically, the control LSI transmits data from a built-in transmitter (Tx) to parallel signal lines and the reception-side driver LSI receives data from the parallel signal lines by means of a built-in receiver (Rx). In the case of small size LCD modules, a controller LSI with a built-in transmitter (Tx) may not be mounted in the LCD module.
Japanese Unexamined Patent Application Publication No. 2001-144620 discloses a technology that, in a bus system that performs parallel data transmission via a plurality of signal lines, the occurrence of crosstalk noise on the plurality of signal lines is decreased by reducing the frequency of occurrence of “0” or “1” contained in the transmitted parallel data.
FIG. 6 is a circuit diagram showing part of the transmission side of the bus system that appears in Japanese Unexamined Patent Application Publication No. 2001-144620. Hereinbelow, with reference to FIG. 6, a bus system that appears in Japanese Unexamined Patent Application Publication No. 2001-144620 will be described briefly.
In the case of the bus system that appears in Japanese Unexamined Patent Application Publication No. 2001-144620, transmission-side EXOR gates 80 to 82 supply transmission parallel data D00 to D02 to a plurality of signal lines. The interface between the transmission side and the plurality of signal lines is thus a CMOS (voltage) method interface.
On the transmission side, AND gates 83 to 85 and a NOR gate 86 judge whether the number of data representing “0” in the parallel data scheduled for transmission is greater than the number of data representing “1”. The EXOR gates 80 to 82 then control inversion of the parallel data scheduled for transmission on the basis of the judgment result outputted by the NOR gate 86 so that the frequency of occurrence of “0” or “1” in the parallel data is reduced.
Therefore, an output of the EXOR gates 80 to 82 reduces the frequency of occurrence of “0” or “1” and hence there is a lower probability of a change in the output of the EXOR gates 80 to 82. For this reason, the occurrence of crosstalk noise in the plurality of signal lines decreases.
In LCD modules that perform parallel data transmission, the volume of data transmitted has increased greatly due to the increased number of grayscales and higher resolution of the LCD modules. Therefore, in LCD modules that perform parallel data transmission, the number of transmission lines required for data transmission has increased, the transmission frequency has risen, and the total current flowing through the signal lines has increased.
The problem of the large total current flowing through the signal lines is not limited to LCD modules handling parallel data. It is common to electronic devices performing parallel data transmission.
Further, in the case of the bus system appearing in Japanese Unexamined Patent Application Publication No. 2001-144620, the probability of a change in the output of the EXOR gates 80 to 82 is reduced. Thus, a decrease in the switching current for changing the output of the EXOR gates 80 to 82 can be expected.
However, in the case of the bus system that appears in Japanese Unexamined Patent Application Publication No. 2001-144620, there is no specific mention of a reduction in the total current flowing through the signal lines.
It has now been discovered that, conventional data transmission device is unable to decrease total current flowing through the signal lines.